Chapter 6: Proteins and amino acids

Question 1

Describe amino acids

Answer 1

• contains nitrogen
• 20 amino acids but 8 are essential
• joined by peptide bonds to form proteins (formed due to loss of water molecule)
• smallest functional units of proteins
• General structure: a carbon atom with an amine and carboxylic and hydrogen attached to it along with a side chain

2 aa: dipeptide
3 aa: tripeptide
>3 aa: polypeptide

Question 2

Where does the denaturation of protein take place?

Answer 2

Stomach

Question 3

How is protein digested and absorbed?

Answer 3

• gastric acid in the stomach denatures and pepsin breaks some peptide bonds
• in the small intestine lumen, pancreatic enzymes break polypeptides to di and tripeptides
• enzymes break di and tripeptides to single aa
• intestinal cells absorb aa and some peptides and release them to the bloodstream (absorbing large peptides causes food allergy)
• carried to liver where it is used or released to blood
• body can reconnect aa to make proteins for energy

Question 4

What are some functions of proteins?

Answer 4

• Growth and maintenance
• Hormones and enzymes
• Antibodies
• energy (secondary function)

Question 5

What are proteins used for?

Answer 5

• converted to vitamins
• converted to other aa
• gluconeogenesis (removal of amine group)
• lipogenesis

Question 6

When are aa wasted?

Answer 6

• energy is lacking
• overabundance of protein
• aa is oversupplied
• diet has too few essential aa

Question 7

What is the DRI for proteins?

Answer 7

minimum: 10% total energy
maximum: 35%

Question 8

What factors influence protein quality?

Answer 8

• digestibility (animal protein is absorbed better than plant protein)
• amino acid composition

Question 9

What are complementary proteins?

Answer 9

> 2 proteins whose amino acid structures supply the essential amino acids missing

Question 10

How to measure protein quality?

Answer 10

• Protein digestibility-corrected aa score (PDCAAS)

- scale of 0-100

Question 11

Who would have a positive nitrogen balance?

Answer 11

• growing child

- pregnant woman

Question 12

Who would have a negative nitrogen balance?

Answer 12

• surgery patient

- astronaut

Question 13

What are the two types of protein-energy malnutrition?

Answer 13

• Marasmus

- Kwashiorkor

Question 14

What is the difference between marasmus and kwashiorkor?

Answer 14

• marasmus is gradual and kwashiorkor is acute
• marasmus <2 years old and kwashiorkor is 1-3 years old
• marasmus is total diet deficiency and kwashiorkor is protein deficiency
• marasmus- no edema kwashiorkor- edema

Question 15

What happens when there is excess protein intake?

Answer 15

• obesity
• increased saturated fat
• kidney and liver problems
• calcium loss

Question 16

What are the different types of vegetarians?

Answer 16

Vegetarian: plant foods with some animal foods eliminated
Vegan: strict veg
Lacto-ovo-vegetarian: dairy and eggs but no seafood or flesh
Lacto-vegetarian: dairy but no eggs, seafood or flesh
Ovo-vegetarian: eggs but no milk products, flesh or seafood
Partial vegetarian: no red meat
Pesco-vegetarian: fish but no red meat or poultry
Macrobiotic diet: gradually eliminates all foods and leads to malnutrition and death